In a process of forming a gate structure using a semiconductor technology, a gate dielectric layer such as a silicon oxynitride (SiON) is formed on a substrate, and then a polysilicon layer is formed on the gate dielectric layer. Generally, a single wafer tool or a furnace tool is applied so that the polysilicon layer is formed by using a single deposition step. Before forming the polysilicon layer, an annealing process is conventionally performed. However, during the annealing process, a number of nitrogen atoms inside the gate dielectric layer diffuse in the gate dielectric layer to lose out of the gate dielectric layer, which is called an out-gassing phenomenon. Due to the loss of the nitrogen atoms of the gate dielectric layer, a dielectric constant of the gate dielectric layer is decreased. In other words, if the gate dielectric layer wants to have a desired dielectric constant, a thickness of the gate dielectric layer will be increased. In addition, a leakage current of a semiconductor component with the polysilicon layer using the conventional method will increase, thereby reducing the reliability of the semiconductor component and affecting the performance of the semiconductor component.
Therefore, what is needed is a gate structure and a method for forming the gate structure to overcome the above disadvantages.